Endless chain drive conveyor systems for moving bulky items through a manufacturing or assembly plant are well known. Such conveyor systems often take the form of "power and free" conveyors which include a "power" and a "free" conveyor track, generally disposed vertically with respect to each other. Operating within the power track is an endless drive chain with drive dogs periodically attached to the chain and extending toward the free track. These drive dogs are oriented to engage a trolley dog or actuator on a drive trolley operating within the free track. While the drive dogs are generally fixed in position relative to the drive chain, the trolley dogs on the drive trolleys are typically selectively retractable.
The free track generally follows the same path as the power track(s) but is spaced vertically relative thereto. As originally implemented, power and free conveyor systems were suspension systems with loads suspended from trolleys or carriers operating in the free track and with the power track disposed above the free track. These suspension systems have reached a high degree of sophistication and can include features such as the ability to stop and accumulate free trolleys in specific accumulating areas and transfer zones which include intersections where loads can be transferred between non-synchronous conveyor systems.
More recently, in response to the specific requirements of the automobile industry, floor mounted or "inverted" power and free systems have been developed. In these inverted systems, the power track and the free track are disposed beneath the floor of the factory, with the free track positioned above the power track. A plurality of load carriages are attached to the free trolleys through a slot in the factory floor. Each load carriage is usually attached to two or more load carrying trolleys with the load carriage being disposed above the floor and driven along the conveyor path by the associated load carrying trolleys.
These inverted systems have the capability of handling bulkier and heavier loads, such as automobile chassis, while minimizing many dangerous conditions found in suspension systems. For example, inverted systems allow workers to safely climb on and off of the load carriages and they eliminate the danger inherent in the swinging loads of suspension systems.
In both suspension and inverted power and free conveyors, the endless drive chain must be adjusted to provide optimum chain tension in the power track. This is done by routing the chain around a large chain take-up pulley which is mounted on a movable carriage. The drive chain enters from a first side of the carriage, makes a 180 degree loop around the take-up pulley and exits the first side of the carriage. A second side of the carriage opposite the first side is connected to a double action take-up pneumatic cylinder and piston via a clevis and chain. The take-up pneumatic cylinder is anchored in place such that, by retracting the piston, the movable take-up carriage is pulled toward the pneumatic cylinder, thus tensioning the chain. The pneumatic cylinder is typically supplied with a constant air pressure to assure a uniform chain tension in the conveyor.
It is important for a variety of reasons to know the position of the take-up carriage. For example, a drive chain for which too much take-up is required to maintain operating tension might be fatigued in whole or in certain links. On the other hand, in the event of failure of the take-up cylinder or the compressed air supply, should all chain tension be lost, a dangerous condition could occur in the conveyor. In order to indicate take-up position, a plurality of limit switches can be positioned alongside the pneumatic take-up cylinder. An actuator rod is oriented in parallel to the pneumatic cylinder piston and is connected to the piston for movement therewith. The actuator rod extends into and is movable relative to a holder which holder is stationary with respect to the pneumatic cylinder. A limit switch actuator flag is attached to the actuator rod such that the limit switches are actuated in turn as the take-up piston is extended or retracted. Indicators and/or conveyor shut downs are connected to be controlled by the limit switches.
During maintenance and repair operations on the conveyor, it is typical for the take-up tension to be released with the chain connecting the take-up carriage to the take-up piston disconnected and then reconnected. Often the chain will be inadvertently twisted, rotating 180 degrees or more at the connecting link, a condition which is difficult to detect. Once the take-up piston is retracted again to reestablish the required chain tension, the several tons of pressure on the take-up chain causes the chain to untwist, at least partially, and often in a violent motion. This untwisting, rotary motion of the take-up chain is transmitted to the take-up piston, which can readily absorb a certain amount of rotary motion. The problem lies in the actuator rod which is attached to the piston. As the piston is rotated, a tremendous amount of torque is imparted to the actuator rod, resulting in a violent twisting motion on the actuator rod. Typically the actuator rod will bend or even break under such a force, rendering the actuator flag and the position sensing limit switches inoperative.
It is clear then, that a need exists for an improved limit switch actuator rod and an improved connection between the actuator rod and the chain take-up pneumatic cylinder piston in a power and free conveyor system. Such a limit switch actuator and connection should prevent damage to the actuator rod from any twisting motion imparted to the pneumatic piston.